STORY ARCHIVE

Death Star - Part 1

This is part one of a two part journey to the beginning of our universe. Out in deepest space lurks a force of almost unimaginable power. Explosions of extraordinary violence, are blasting through the Universe every day.

If one ever struck our Solar System it would destroy our Sun and all the planets. For years no one could work out what was causing these awesome explosions. Now scientists think they have identified the culprit. It's the most extreme object ever found in the Universe; they have christened it a 'hypernova'.

It was not until 1997, when a satellite pinpointed the exact location of these bursts, that scientists began to solve the puzzle. It seems these huge explosions are caused by the death throes of stars twenty times the size of our Sun, which burn themselves out and explode, creating hypernovae. What then unfolded was a chain of events, which would ultimately point towards some of the most exotic wonders in the Universe: stellar nurseries (where new stars are born) and black holes.

Observations show that - instead of fading away, as an explosion might be expected to - radiation continues to emerge from the area of a hypernova. This ongoing emission is characteristic of the process of star birth. Astronomers conclude that the hypernova grows rapidly along with other normal stars in a nursery, but burns out when its contemporaries are still in their infancy.

Find a hypernova, therefore, and you have also tracked down a part of space where stellar synthesis is underway. Which is why some scientists now believe that the huge explosions of hypernovae may be the key to unlocking one of the great unsolved mysteries in the Universe: how the first stars were made at the very dawn of time.

TRANSCRIPT

Narrator: (John Shrapnel): Out there in the depths of space lurks something so deadly it destroys everything in its path. Explosions of inconceivable power are tearing through the universe hundreds of times a day. For years science has been on a quest to find out what was causing these explosions and now, at last, they may have found the answer. What they have discovered is that these forces of destruction may hold the key to one of the great secrets of creation – how you and I came to be.

When we look up at the night sky we see thousands of stars shining brightly. In fact, there are billions upon billions of stars stretching across the universe, but it wasn’t always this way. Once there was a time when there were no stars. There was nothing to light up the sky. This time of darkness was just after the Big Bang 14 billion years ago.

Prof. Martin Rees: The entire universe started off as a hot fireball and it cooled down and after about half a million years our universe entered a literal Dark Age. The universe then stayed dark until the first stars formed and lit it up again.

Narrator: Lost inside this cosmic Dark Age is one of the great mysteries of science: the very first stars, the creators of everything. Stars are the factories of the universe. Inside their burning cores all the elements that make up everything we see and touch today are created, but without those very first stars to begin this process of creation there would be no galaxies, no Earth, no us. A great puzzle at the heart of this creation story is if the stars create everything then how were the very first stars themselves created all those billions of years ago? It is a mystery that has baffled scientists for generations.

Dr Nial Tanvir: A very difficult question is trying to work out how those, those early stars formed. It’s a very difficult theoretical question because we don’t have observations to guide us.

Narrator: There are no observations because there is not enough light to see back into the cosmic Dark Age when it all began and light is what astronomers need to see back in time. Sunlight takes eight minutes to travel to Earth. When we look up at the Sun we see it as it was eight minutes ago and when we see the light from other stars from further away we are in fact seeing further and further back in time, so when we look at a star from the other side of our galaxy 100,000 light-years away we’re really seeing it as it was when the light left it 100,000 years ago.

Dr Nial Tanvir: As we look out across the universe at the most distant objects that we can see we’re actually going backwards in time, looking backwards in time billions of years.

Narrator: But no matter how hard we look no-one has been able to see back to the cosmic Dark Age - until now. Something has been discovered that may light up the darkness of the early universe and solve the mystery of how the very first stars were made, something that sends science on a quest that would span the entire universe.

Prof. Stan Woosley: Who would have thought that this journey would take us to the edges of the universe, the biggest explosions in nature, black hole birth, star death, just the most exotic phenomena that I’ve ever seen and I’ve been studying explosions all my life.

Narrator: The journey began over half a century ago with a bizarre chain of events at the height of the Cold War.

Man: Attention all bases, attention all bases, this is Ironhand, this is Ironhand. This is a shock alert. I repeat, this is a shock alert.

Narrator: It was the 1950s and the world was gripped by fear. The Americans were convinced the Russians were trying to develop nuclear weapons behind their back and because they thought the Communists are devious they decided that the most likely testing site for these new weapons were not in the oceans, not in the deserts, in fact not even on earth itself. The Americans believed the Soviets were testing nuclear bombs on the dark side of the Moon.

Stirling Colgate: I mean come on, give me a break type of thing nowadays. The ridiculousness of it, the, the, but the Soviets would buy into the same paranoia because their paranoia was, you know, might say more deeply inbred.

Narrator: Stirling Colgate was an expert in nuclear bomb testing. He was put in charge of designing a series of satellites sensitive enough to pick up even the faintest trace of a nuclear explosion from as far away as the Moon.

Stirling Colgate: So the satellites were made to detect nuclear violators, cheaters, which meant they had to be a great deal more sensitive than any sensible bomb physicist would have ever said they needed to be.

Narrator: Colgate’s satellite was designed to pick up the one telltale sign of a nuclear explosion that not even the Russians could hide.Gamma rays, the deadliest form of energy in the universe.

Prof. Stan Woosley: A typical gamma ray can go through about that much lead and that means a good, good number of them will deposit in your body and they can do biological damage.

Narrator: With every nuclear explosion there is a deadly blast of gamma rays. If the Communists were testing bombs on the Moon then Stirling Colgate’s satellite would spot them. Colgate’s satellite was launched amidst great secrecy, but what it would discover would turn out to be far more deadly than a Russian nuclear bomb. On 2 July 1967 it seemed their worst nightmare had come true. Colgate’s satellite picked up a huge burst of gamma rays.

Stirling Colgate: A nuclear bomb signal that you’d expect to see from a test in space of a nuclear weapon would be first a pulse, smaller pulse, then followed by some time a much bigger pulse and these two pulses are the primary and the secondary.

Narrator: But the tell-tale signal was not from any nuclear bomb. It was from something far, far bigger, something of incomprehensible size.

Stirling Colgate: I was blown away, totally, completely blown away. My, my God, what the hell are they seeing out there?

Narrator: And the signals just kept on coming. Something out there was causing huge explosions blasting out deadly gamma rays.

Prof. Stan Woosley: No-one really knew quite what to make of it and there were, there were preposterous ideas bandied around for a while that even these were inter-stellar star wars going on and we were seeing the, the phaser blasts that missed their target, or that comets were annihilating with anti-comets or little black holes were evaporating. People didn’t quite know what to make of it.

Narrator: The journey that would one day lead science back into the cosmic Dark Age had begun. Astronomers were baffled. They had no idea what was causing these bursts. The most likely cause, they thought, was some kind of exploding star, but to be sure they turned to no less an authority than Einstein and to one of the most fundamental of all the laws of physics:

E = MC2. This famous equation under-pins many of our assumptions about how the universe works. It puts a limit on the size of any explosion. Nothing can explode with more energy than is contained in its mass, so if some kind of star really was the source of these gamma ray bursts then E = MC2 would tell you how big the explosions could be.

Prof. Martin Rees: The amount of power you can get from a staris limited, according to Einstein’s famous formula E = MC2 and if you know M, the mass, which you do know for stars, then we know the maximum amount of energy which you could get by any conceivable process.

Narrator: Once they knew there was a finite size to these explosions they could then work out how far away they were. When they plugged in the numbers they realised that these explosions must be happening in our very own galaxy. Any further away and E = MC2 would be broken. The explosions would be bigger than was physically possible for any star to produce and so they scoured the galaxy to find out what kind of star could be causing these bursts of gamma rays and before long they thought they’d found the culprit. Neutron stars are amongst the most powerful objects in our galaxy. They are so dense that they have a gravitational pull of such strength that if anything strays too close it is dragged onto the star with extreme force.

Chip Meegan: A neutron star is typically just a few miles across and will have a mass as great as the Sun so the densities are just enormous. If you dropped a marshmallow onto a neutron star it would have the energy of an atomic bomb because the gravity is so powerful.

Narrator: Neutron stars seem to contain enough energy to produce these gamma ray bursts. The only question was: what was actually triggering them?

Chip Meegan: There were a number of ideas relating to neutron stars specifically. The idea was you dropped something onto the neutron star and it releases a lot of energy. One idea was an asteroid falling on a neutron star.

Narrator: It soon became the accepted theory that neutron stars fired off these bursts of gamma rays if something collided with them. The mystery seemed to be solved. Now they had the answer everyone began to speculate about the possible impact of these bursts on Earth. It began to dawn on them that if these explosions were coming from our own galaxy in effect they were occurring right next door to us.

Chip Meegan: If a burst did go off in our own galaxy it would be quite spectacular, it would be extremely bright anywhere in the galaxy and if we were close enough I suppose it could do quite a bit of damage. Some people have hypothesised that major extinctions are the result of gamma ray bursts in our own galaxy.

Narrator: While they worked out that the odds of Earth being hit again were extremely remote, if it did happen the effects would be devastating.

Prof. Stan Woosley: Suddenly there would be a light in the sky. If it was 300 light-years away, a million times brighter than the Sun. This would be the equivalent of one million megaton bombs going off all over the Earth at the same time.

It would be Hiroshima all over the world. The atmosphere of the Earth would be heated, there would be gigantic hurricanes, cyclones, tidal waves every form of destruction you can imagine. This may have happened to some civilisations somewhere in our galaxy probably did, but the likelihood that it will happen to us in the next million years is comfortably very small.

Narrator: The Earth, it seemed, was safe, but what no-one could have known was that what was really under threat was something far, far more fundamental. Bohdan Paczynski was an astronomer more interested in facts that the complex theories of the time. He decided to concentrate only on what he could actually see, the direction the bursts were coming from and their distribution across the sky.

Prof. Bohdan Paczynski: When I look at gamma ray burst I realised, at least for me, it was hopelessly complicatedso I gave up on that instantly. I just thought it’s far too difficult for me and instead I looked at things, aspects of gamma ray bursts, which are easy to comprehend and this are the distribution properties.

Narrator: To plot the direction of the bursts Paczynski turned to our galaxy – the Milky Way. When we look up at the night sky we see the Milky Way as a narrow streak of stars. Astronomers call this area of the sky the galactic plane, but ours is a distorted view because we sit at the very edge of the galaxy. In fact our galaxy stretches for 100,000 light-years across space in a flat disc. If these bursts really were coming from within our galaxy then Paczynski realised they should all be coming from just one place.

Prof. Bohdan Paczynski: If gamma ray bursts were in our galaxy they should be distributed the way everything is distributed now our galaxy which means they should be near the galactic plane and possibly also concentrated towards the galactic centre.

Narrator: But when he pieced all the available data together what Paczynski saw was something quite unexpected.

Prof. Bohdan Paczynski: Gamma ray bursts were coming to us fromall over the sky with no particular relation to our galactic plane or the galactic centre and in fact that is what I saw in the data.

Narrator: So the gamma ray bursts were not coming from the area of the Milky Way. They were coming from all over the night sky. To Paczynski this could only mean one thing.

Prof. Bohdan Paczynski: Contrary to popular belief gamma ray bursts could not possibly be in our galaxy, but instead they should be very, very far away, sort of at the edge of the universe.

Narrator: Paczynski had thrown down a challenge. The neutron star theory, he declared, was wrong. The explosions had to be coming from something far bigger and far further away. The problem was that Paczynski’s observations seemed to require explosions with more energy than any star had ever produced.

Prof. Stan Woosley: If you took a model that would work at the distances Bohdan was describing you would have to convert a million Earth masses into pure energy instantaneously - well within 10 seconds anyway - and in the form of gamma rays and get it out and get it three billion light-years to us and so yeah, OK, Bohdan may be, but be good, work on something else for a while.

Narrator: When Bohdan Paczynski released his results he was dismissed as mad.

Prof. Bohdan Paczynski: Those people who noticed thought oh my goodness, he’s crazy it’s not a serious proposition. We don’t believe it because this would require outrageous amount of energy if you put those sources so far away they would have to be unbelievably energetic in order to, for us to see them at the intensity we see them so basically that was completely dismissed.

Narrator: The only way Paczynski could be right was if Einstein was wrong and E = MC2 was wrong. Paczynski must have made a mistake. He was soon forgotten and so was his theory, until five years later when he was to return with a vengeance. In 1991 NASA launched the Batse satellite. Equipped with state-of-the-art detectors, it was going to study the bursts in detail for the first time, but as the data came in a disturbing picture began to emerge. What they’d expected was that the bursts would line up with the galactic plane meaning they were coming from within our own galaxy.

Jerry Fishman: The first dozen or so gamma ray bursts weren’t lining up with the, the galaxy. The next dozen or so also weren’t lining up with the galaxy, but they happened to be randomly distributed throughout the sky.

Narrator: Once again the first thoughts of the scientists were that someone must have made a mistake.

Chip Meegan: I think the immediate reaction was perhaps a little bit of disbelief that they must be doing something wrong and of course ourselves, we were worried about that, and worried about it every night when we tried to sleep.

Narrator: And yet as every day went by more and more bursts appeared all over the sky.

Jerry Fishman: We said well, this is going to cause a lot of waves, but we better go public with this announcement that it looks like the gamma ray bursts are uniformly distributed throughout the sky.

Narrator: There was now no doubt. Paczynski had been right all along.

Prof. Bohdan Paczynski: I think that was professionally the most joyous moment in my life because all of a sudden I realised that something which was very risky, which could work either way, turned out my way, so of course I was very, very happy.

Narrator: But Paczynski’s triumph threatened to plunge science into chaos. If the bursts were coming from beyond our galaxy then they had to be caused by something far bigger than science could explain.